1. Field of the Invention
The invention relates to an optical viewer instrument with a photographing function.
2. Description of the Related Art
As is well known, an optical viewer instrument, such as a binocular telescope, a single telescope or the like, is used for watching sports, wild birds, and so on. When using such an optical viewer instrument, it is often the case that the user sees something that he or she would like to photograph. Typically, he or she will fail to photograph the desired scene because he or she must exchange a camera for the optical viewer instrument and during this time the chance is lost. For this reason, an optical viewer instrument containing a camera is proposed, whereby a photograph can be taken immediately by using the camera contained in the optical viewer instrument while continuing the observation through the optical viewer instrument.
For example, Japanese Laid-Open Utility Model Publication (KOKAI) No. 6-2330 discloses a combination of a binocular telescope and a camera, in which the camera is simply mounted on the binocular telescope. Of course, the binocular telescope includes a pair of telescopic lens systems, and the camera includes a photographing lens system. While an object is observed through the pair of telescopic lens systems, the observed object can be photographed by the camera.
In general, a telescopic lens system includes an objective lens system and an ocular lens system which are associated with each other, and an object at infinity is brought into focus when a rear focal point of the objective lens system and a front focal point of the ocular lens system substantially coincide with each other. Thus, to bring a near object into focus, it is necessary to relatively move the objective lens system and the ocular lens system away from each other. Namely, a focussing mechanism must be incorporated into the telescopic lens system before the near object can be brought into focus.
For example, in a binocular telescope, the focussing mechanism is formed as a movement-conversion mechanism, having a rotary wheel, which converts a rotational movement of the rotary wheel into a relative translational movement between the objective lens system and the ocular lens system included in each telescopic lens system. Namely, in the binocular telescope, a near object is brought into focus by manually rotating the rotary wheel.
In the binocular telescope with the camera, disclosed in the aforesaid Publication (KOKAI) No. 6-2330, both the telescopic lens systems serve as an optical view finder system for the camera, and thus an object, observed through both the telescopic lens systems, is photographed by the contained camera. Nevertheless, the aforesaid Publication (KOKAI) No. 6-2330 makes no reference to focussing the contained camera.
U.S. Pat. No. 4,067,027 discloses another type of binocular telescope containing a camera using a silver halide film. In this binocular telescope with a camera, a first focusing mechanism is incorporated in a pair of telescopic lens systems to bring an object into focus, and a second focusing mechanism is incorporated in a photographing lens system of the contained camera to bring the object into focus. The first and second focusing mechanisms have a common rotary wheel, and are operationally connected to each other so as to be operated together by manually rotating the common rotary wheel. Namely, when the object, observed through the telescopic lens systems, is brought into focus by the operation of the first focussing mechanism, the observed object is focussed on a frame surface of the silver halide film through the photographing lens system by the operation of the second focussing mechanism.
In general, in the field of cameras using a silver halide film, a focussing mechanism for a photographing lens system must be designed such that the degree of unsharpness of an optical image, which is obtained through the photographing lens system, falls within a permissible circle of confusion, before the optical image can be properly brought into focus through the photographing lens system. As is well known, the permissible circle of confusion is mainly determined by the characteristics of the photosensitive material used in the silver halide film. For example, in a 35 mm silver halide film, it is said that a diameter δ of the permissible circle of confusion is approximately 30 μm or approximately 1/1000 of a diagonal line length of a film frame, taking resolution ability of typical person into consideration.
Also, a focal depth of the photographing lens system is defined based on the diameter δ of the permissible circle of confusion, as follows:FOCAL DEPTH=2×δ×F Herein: “F” represents an f-number of the photographing lens system.
Thus, an object to be photographed must be focussed within a range of the focal depth as defined above, before the photographed object can be obtained as a properly-focussed image. The focal depth of the photographing lens system is variable in accordance with the above-mentioned parameters (δ, F) and the photosensitivity of the silver halide film. When the range of the focal depth is too narrow, it is very difficult to bring the object into the too-narrow-range of the focal depth by the manual operation of the focussing mechanisms.
U.S. Pat. No. 4,067,027 discloses the manually-operated focussing mechanisms, but it refers to no specifications of the telescopic lens systems and the photographing lens system which are suitable for the manual-operation of the first and second focussing mechanisms. Thus, it is impossible to ascertain if the focussing of both the telescopic lens systems and the photographing lens system can be achieved by manually operating the first and second focussing mechanisms.
On the other hand, when a digital camera, using a solid-state image sensor, such as a CCD (Charge-Coupled Device) image sensor, is incorporated in an optical viewer instrument, such as a binocular telescope, a single telescope or the like, and when both a telescopic lens system and a photographing lens system are manually focussed, in addition to the above-discussed matters, other specific issures, involving the solid-state image sensor, must be taken into consideration in the optical design of both the telescopic lens system and the photographing lens system, before satisfactory manual focussing of both the telescopic lens system and the photographing lens system can be ensured.
In short, conventionally, it has not been proposed how an optical viewer instrument with a photographing function should be designed so that a focussing of the photographing lens system can be suitably and properly performed with a desired focussing accuracy, in a manual focussing manner.
In addition, the binocular telescope with the camera, as disclosed in the aforesaid Publication (KOKAI) No. 6-2330 is bulky, because the camera is simply added to the binocular telescope. Also, in U.S. Pat. No. 4,067,027, the camera used is bulky because of the camera box for housing a silver halide film cartridge.